Thank you so much for bringing this to our attention. I apologize for the delay. I have shared this with the support staff to look into at their earliest convenience. Your patience is greatly appreciated!

- Do npm install @sencha/ext-react in a empty directory
- Open ExtRenderer.js in the src/ folder or dist/
- Go to line 428, doAdd function. Notice the childXtype argument
- Go to line 440, notice that is trying to access childxtype